It is very difficult and usually quite expensive to provide an explosive composition which is stable and reliable when charged into blast holes which are either damp or contain water. Many explosive compositions, as used in damp environments, require that the composition itself be packaged in plastic bags or the like to prevent water degrading the explosive mix. This results in costly packaging methods which require special handling care. As appreciated, should the bag structure be perforated or in some way damaged, the explosive contents can be spoiled by water.
A water resistant explosive composition is disclosed in Canadian patent No. 877,227. The composition comprises in combination ammonium nitrate prills mixed with a solution of ammonium nitrate in combination with a setting agent, such as alkaline earth metal oxides. The composition, as mixed, is allowed to set and harden in the shape of the mold into which it is poured. The hardened composition can then be of a shape which will permit introduction to blast holes and the like for purposes of blasting. This type of composition has to be made at a full scale plant and must be cast into desired shapes. The material does not lend itself then to the shape of the cavity into which it is introduced and hence ineffective blasting occurs.
It is appreciated that there are a wide variety of explosive slurries available for use in blasting operations. However, such slurries usually tend to have low water resistance and degrade if left too long in a blast hole which either admits water or contains water. Such explosive slurries are usually made with the use of gelling and/or thickening agents which include natural gums and synthetic gels, such as polyacrylamides and the like. An example of such blasting slurries is disclosed in Canadian patent No. 933,780.
In Canadian patent No. 888,102, water resistivity is imparted to an explosive composition by use of synthetic gelling and/or thickening agents. The thickening agents may include suitable gums, such as guar gums which are cross-linked by a cross-linking agent such as sodium dichromate or a saturated solution of ammonium nitrate in liquid ammonia (Divers liquid). The composition, as prepared in accordance with this patent, is a dry explosive composition consisting in admixture of ammonium nitrate prills with particulate light metal, a detonable organic sensitizer and a thickening agent. However when such compositions are introduced into water filled blast holes, the ammonium nitrate prills tend to degenerate.
Other forms of water resistant explosive compositions are disclosed in Canadian patent No. 804,541. This patent discloses coating ammonium nitrate prills with metalic stearates or oleates to which fuel oil is blended. The mixture is subsequently blended with ammonium nitrate solutions containing guar gums which, after blending with the coated ammonium nitrate prills, is cross-linked with ammonia to provide a waterproof paste slurry or emulsion depending on the rate of mixing and the amount of ammonium nitrate solution used. Olney, U.S. Pat. No. 4,138,281, discloses an emulsification of hot ammonium nitrate solutions using fuel-oil and wax carriers with an organic stearate or oleate as an emulsification agent. To sensitize this composition, micro air bubbles are added chemically or physically using microspheres of glass borates, etc. Both of these explosive compositions contain water, possibly as high as 20%. As water does not explode, considerable energy is taken out of the system. In practice, such compositions have been blended with straight ammonium nitrate fuel-oil blasting materials to reduce cost of compounding. This practice results in the velocity of detonation being lowered to that of the inferior ammonium nitrate fuel-oil blasting compositions.